As an apparatus for converting a translational motion into a rotational motion, or the rotational motion into the translational motion, there has been known a screw motion mechanism including a threaded shaft provided with helical male threads and a nut member provided with female threads and threadedly engaged with the threaded shaft. In particular, a ball screw apparatus including balls interposed between the threaded shaft and the nut member is used for various purposes. For example, as disclosed in Patent Literature 1, there has been known a ball screw apparatus used, for example, in a damping apparatus for quickly diminishing vibration to be applied to building structures.
This damping apparatus is an apparatus provided as a brace between poles of building structures. Specifically, the damping apparatus includes a rod member coupled to one structural body, and a housing member provided to cover the rod member and fixed to another structural body. The rod member has an outer peripheral surface provided with a helical thread groove, and a nut member that is freely rotatable with respect to the housing member is threadedly engaged with the thread groove. In other words, the rod member corresponds to the threaded shaft of the ball screw apparatus. Further, a cylindrical rotor housed within the housing member is fixed in the nut member, and the rotor has an outer spherical surface facing an inner peripheral surface of the housing member so as to form a containing chamber for viscous fluid.
In the damping apparatus structured as described above, when the rod member advances and retracts in an axial direction with respect to the nut member along with vibration applied between the two structural bodies, the nut member converts an axial motion of the rod member into a rotational motion, and the rotor fixed in the nut member is also rotated along with the rotational motion of the nut member. A gap between the outer peripheral surface of the rotor and the inner peripheral surface of the housing member is formed as the containing chamber for the viscous fluid. Thus, when the rotor is rotated, a shear friction force in proportion to a rotational angular speed of the rotor is applied to the viscous fluid in the containing chamber. As a result, beat is generated in the viscous fluid. In other words, in this damping apparatus, vibrational energy between the structural bodies is converted into energy of a rotational motion, and further, energy of the rotational motion is converted into thermal energy. As a result, the vibrational energy transmitted between the structural bodies is damped.
The damping apparatus is used by fixing one end of the housing member and one end of a threaded shaft as the rod member respectively to separate structural bodies. In this case, in order to allow postural changes of the damping apparatus with respect to the structural bodies, the housing and the rod member are connected respectively to the structural bodies through intermediation of clevises. Those clevises each include a support shaft, and the housing member or the rod member is connected to the structural body while being provided with a degree of freedom to pivot about the support shaft. In this case, the support shaft functions as a rotation stopper for the threaded shaft. With this, a translational motion in the axial direction of the threaded shaft is converted into a rotational motion of the nut member.